1. Field of the Invention
The invention relates to a process and a device for detecting extraneous substances and extraneous fibers in a fibrous composite.
2. Description of the Related Art
From EP 0 744 478, for example, a device for extraneous fiber detection on an opening machine is known, with the aid of which fibers in a fiber-opening line are examined for deviations in color by means of colour sensors. This takes place in the region of an opening roller, where the fibers rest on or against the opening roller in a very loose composite.
From WO 93/13407 a process for identifying extraneous fibers in a moving yarn is known, in which light is thrown onto a stationary point on the yarn and a number of sensors pick up the reflected light and the transmitted light.
From EP 0 679 599 a fiber band monitoring arrangement is known, which has the function of detecting a break in the fiber band and in which the transport movement of the band is detected by a sensor.
From GB 1 211 463 a test apparatus is known, with the aid of which it is possible to identify, in the laboratory, extraneous fibers in a band made of fibers. In this apparatus, the band is pressed flat and fanned out so that it subsequently forms only a comparatively thin layer, which can be transilluminated.
The known processes and devices each have specific disadvantages, depending upon their construction and the place in the production line at which they act. If the identification or detect-on of the extraneous fibers and extraneous substances takes place in the yarn, the only possibilities available are either to cut out portions of yarn contaminated by extraneous fibers or extraneous substances, something which interrupts production of the yarn and results in splices in the yarn when the latter is put together, or else to leave the contaminants in the yarn. Considerable lengths of yarn may be affected, depending upon the nature of the contamination. If the identification or detection takes place too early in production, for example in the opening machine, it is often possible to remove contaminants only by also centrifuging out fairly large quantities of the non-contaminated fibrous composite with them. In this connection, however, it is also possible for the contamination to occur in such an attenuated manner that it may possibly not be identified by sensors at all, because set threshold values are not reached by the sensor signals. If it is desired to identify contaminants still earlier, for example when the fibrous material occurs in flocks, contaminants may possibly not be identified at all because they are concealed inside the flock. If contaminants and extraneous fibers are ascertained in known manner in the band, the latter must be centrifuged out of the current production and is altered to such an extent, for measurement or examination purposes, that it can be said to be destroyed.